Lift More, Lose More

If you want to slim down and sculpt sexy muscles, then put away those five-pounders. A study published in Medicine & Science in Sports & Exercise showed that women who lifted a challenging weight for eight reps burned nearly twice as many calories as women who knocked out 15 reps with lighter dumbbells. Increasing your workload builds more muscle that torches fat all day long, says Barry Jay, cofounder of Barry's Bootcamp. And because lean muscle is compact, your clothes will fit better, not more snugly.

This workout, designed by Jay, uses "burn-out sets" to make you stronger and firmer. Starting with the first move, do four sets of 10 reps before going on to the next exercise. The key is starting with a weight that makes it tough to finish 10 reps. After those first 10, rest for a minute, then try another 10 reps. If you start losing form, drop down to a lighter weight. After 10 more reps, rest for a minute, then continue for two more sets, gradually dropping weight. Try it two or three times a week.

Exercise 2Curl to Lunge Press

With feet hip-width apart, hold dumbbells, palms facing in. Curl the weights up to your shoulders as you step forward into a lunge. Press the dumbbells overhead, then press through your heel to return to standing. Lower the weights. Repeat with the other leg. That's one rep.

Exercise 4Chest Press and Fly

Lie back on a stability ball, holding dumbbells at your chest, palms facing each other. Push the weights straight up. Open your arms wide, lowering the weights out to the sides and a bit back, until your upper arms are nearly parallel to the floor. Reverse the move to return to start. That's one rep.